1. Technical Field
The present invention relates generally to power converters and more specifically to temperature sensitive power converters for recreational vehicles.
2. Description of Related Art
Lead acid batteries are made up of plates, leads, and lead oxide with a sulfuric acid/water solution. Other elements may be used to change density, hardness, porosity, etc. The acid/water solution is an electrolyte solution which causes an electrochemical reaction that produces an electric current. This electrochemical reaction causes sulfur ions to accumulate on the battery plates. Recharging the battery causes the sulfur to return to the electrolyte solution.
Quickly charging the lead acid batteries employed in recreational vehicles (RVs) over wide ambient temperature ranges, without over or under charging, is a problem that has always plagued the industry. Increasing the initial charging voltage for a predetermined length of time (also known as “rapid charging”) has been somewhat successful. However, the risk of over charge at high ambient temperatures is still a major problem. Reducing the rapid charging time the increased charging voltage is maintained may result in an undercharge condition at low ambient temperatures.
Because ambient temperatures fluctuate significantly during the various seasons, and over different parts of the world, it is impossible to set the time and charging voltage at fixed values and achieve adequate results over such diverse climates. Lead acid batteries are very sensitive to ambient temperature. The ambient temperature affects the current that a battery will accept at a given charging voltage. Another variable that affects the current flow when a charging voltage is applied is the state of charge of the battery. However, determining this variable is not practical in real life as it would require the user to check the specific gravity of the electrolyte of the battery and then to select predetermined charge cycles based on temperature and state of charge before starting the charging process. In general, this method is excellent but would be cumbersome and impractical in the case of batteries employed in recreational vehicles (RVs).
In the past, the output voltage of power converters was set at a nominal 13.8 volts, which was a middle of the road approach that would not overcharge the battery to a great extent at high ambient temperatures of 86° F. (30° C.) while giving the battery a reasonable charge at room temperatures of 77° F. (25° C.). This approach, however, gives less than desirable results when ambient temperatures drop below 68° F. (20° C.).
Based on leading battery manufacturers' recommendations, float voltages (the voltage to maintain the state of charge) range from approximately 13.0 volts at 122° F. to 14.7 volts at 0° F. The recommendation for a deep rapid charge ranges from 13.74 volts at 122° F. to 15.48 volts at 0° F. However, the rapid charge voltages cannot be maintained indefinitely because of overcharge problems.
Therefore, a charging system is needed that automatically adjusts the charging voltage applied to RV batteries based on ambient temperature. A charging system is needed that adjusts the charging voltage to monitor a rapid charge voltage for a predetermined period of time at a voltage level recommended by the manufacturer for the ambient temperature. Further, a charging system is needed that adjusts the charging voltage to maintain a float voltage after the initial rapid charge as recommended by the manufacturer for the ambient temperature.